zoom-cache includes a simple variable-length coding scheme for signed integers.
When decoding, single bytes are read at a time. If the high bit is set, the
next byte is also read. The lower 7 bits of each byte contain data. Decoding
continues by reading single bytes until a byte is read with the high bit zero.

The first byte of a variable-length coded integer contain a sign bit and the
lowest 6 bits of the value. This byte is encoded as: